Rotary vane vacuum pump having a rotor axial seal and an axially bias rotor-drive shaft combination

ABSTRACT

A vacuum pump of the rotary vane type, comprises a casing ( 50 ) having a cylindrical inner wall surface ( 52 ), a first ( 54; 54 ′) and a second ( 56; 56 ′) end wall at opposite sides of said casing defining a fluid cavity therein, fluid inlet ( 60 ) and outlet ( 62 ) ports in open communication with said fluid cavity, and a rotor ( 64; 64 ′) extending between said end walls carried by a drive shaft ( 70 ) for rotation about an axis eccentric to said casing inner wall surface, said rotor being provided with a plurality of longitudinally extending radial slots ( 66 ) about the periphery thereof. Further, there are provided a plurality of vanes ( 68 ), each being radially slidably carried within a respective of said slots. The invention comprises that at least one of said end walls and said rotor comprise, at oppositely facing surfaces, an annular recess ( 84, 86; 84′, 84″, 86′, 86 ″) and an annular rib ( 88, 90; 88′, 88″, 90′, 90 ″), respectively, said rib and recess being interengaging so as to define a radial clearance ( 92, 96; 92′, 96 ′) and an axial seal ( 94, 98; 94′, 98 ′), respectively, between said at least one of said end walls and said rotor, and that the rotor/drive shaft combination is axially biased.

The present invention generally relates to vacuum pumps, and morespecifically to the kind of device in which a plurality of vanes arefitted to slide substantially radially in a respective slot of a rotoreccentrically mounted within a casing.

DESCRIPTION OF RELATED ART AND BACKGROUND OF THE INVENTION

A previously known vacuum pump of such kind is illustrated in FIGS.1a-e. The pump includes a cylindrical-shaped casing or housing 10 whichhas an inner cylindrical wall surface 12 and is closed at its oppositeends by end walls 14, 16 such as by means of machine screws 18 or thelike. As shown, the pump includes circumferentially spaced fluid input20 and output 22 ports intercommunicating the interior cavity. Output 22is preferably held at atmospheric pressure, while input 20 is held at avacuum of about 50 kPa during operation.

The rotor 24 of the pump is provided with a number of elongated vaneslots 26 cut therein from the circumference thereof; and wherein aplurality of vanes 28 are mounted in freely slidable relation withinthese slots. A pump drive shaft 30, provided with an axle spindle 32 forcoupling, is keyed to the rotor 24 and is rotatably mounted in the endwalls 14, 16 as by means of bearings 32, 34. The rotor 24 iseccentrically mounted relative to the cylindrical inner wall 12 of thecasing 10. Accordingly, for efficient operation of a pump of this type,as the rotor turns within the casing it is required for the outboardedges of the vanes 28 to be in pressure-sealing contact with the innersurface 12 of the casing 10 while sliding in slots 26 back and forth;and that pressure losses around the longitudinal ends of vanes 28 androtor 24 permitting escape of fluid to the exhaust, must also beprevented.

To such end, the pump comprises radial seals 35, 36 between the rotor 24and the end walls 14, 16, respectively, and also between the vanes 28and the end walls 14, 16. The rotor is not axially locked, but is freelymovable between the end walls, in order not to exhibit unacceptablelosses caused by e.g. axial slackness of the ball bearings andmanufacturing tolerances of the pump components. Due to such freelymovable mounting, however, the pump is very sensitive to axial forcesand in unfortunate situations such forces may lead to seizing of thepump. Additionally, such radial seals need large amounts of evenlydistributed lubrication in order to work satisfactorily and very preciseclearances 38, 40 of the seals 35 and 36, respectively, have to beprovided and maintained irrespective of variations in the temperature ofthe pump. This may be hard to fulfill due to different length expansionsof casing 10 and rotor 24.

The latter problem has been addressed in the art. For instance, U.S.Pat. No. 2,312,655 issued to LAUCK discloses a rotary impeller type ofvacuum pump, which provides for a precise clearance between the wallsand the adjacent impeller assembly irrespective of the materials of thehousing and of the impeller assembly. The pump includes the main housingof a light weight material, the impeller assembly of a heavier material,and an intermediate housing assembly, being composed of a thin sleevemember of a material having substantially the same characteristictemperature expansion as the heavier material of the impeller assembly,an axially adjustable end plate, and a plurality of coil springs. Thethin sleeve member is arranged between the main housing and the impellerassembly and has a length slightly greater than the overall coaxialdimension of the impeller assembly by an amount exactly equal to thedesired total clearance to be provided. The end plate is arranged toengage at the periphery thereof with the end of the sleeve member andurging the same into such engagement by means of the plurality of coilsprings. In such manner the initially provided clearance is maintainedirrespective of the differential temperature expansion between thehousing and the impeller assembly.

U.S. Pat. No. 2,098,652 issued to BUCKBE discloses a similar type ofvacuum pump provided with annular members arranged in spaces providedbetween the rotor-vane combination and the casing heads of the pump.These annular members are maintained pressed against the end surfaces ofthe rotor-vane combination by means of directing a suitable pressurefluid against the annular members, preferably between annular recessesof the annular members and the casing heads, such that they are forcedto rotate with the rotating rotor-vane combination. The longitudinaldimensions are set such that there will always be a clearance betweenthe rotating parts and the casing heads. Further, the annular membersand the casing heads are provided with a number of interengaging annularribs as a further means of preventing internal leakage.

However, such vacuum pumps comprise additional parts, which make themmore complicated and costly to fabricate. Further, the former pump needsprovision of a plurality of coil springs, and it does not provide formaintenance of the radial clearance if there are spatial temperaturegradients, such as if the impeller was to be more heated than the sleevemember. The latter pump needs the provision of a pressure fluid andseals to prevent such pressurized fluid from leaking into the lowpressure pump chamber. Additionally, there are extensive frictionalmovements between the vanes and the annular members, as these membersare pressed against the vanes, while the vanes are sliding substantiallyradially within their respective slots continuously.

Further, U.S. Pat. No. 4,397,620 issued to INAGAKI et al. discloses arotary compressor including disc-shaped members having a diameterslightly smaller than that of a rotor each disposed on opposite ends ofthe rotor and supported on the same rotary shaft as the rotor forrotation, and two disc-shaped recesses each formed on one of inneropposite end surfaces of a housing for receiving therein one of therotary disc-shaped members. A small gap is formed between the inner endsurfaces of the housing and the end surfaces of the rotor, and smallgaps are formed between surfaces of the rotary disc-shaped members andsurfaces of the disc-shaped recesses.

However, such pump is not suitable to be used with a coupling, whichgenerates axial forces since the pump then may seize. Further, the pumpmay be noisy and the bearings used may be exposed to stress, and thushave a short lifetime. Also, it is doubtful if the pump may withstandits own weight, and maintain the radial gaps if mounted on a supportwhich is not horizontal.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a vacuum pump of therotary vane type, which is in lack of the problems discussed above inconnection with vacuum pumps of the prior art.

It is yet a further object of the invention to provide such a vacuumpump that is efficient, simple, reliable, of low cost, and easy tomanufacture.

It is still a further object of the invention to provide such a vacuumpump that allows for axial biasing of the rotor.

These objects among others are, according to the present invention,attained by vacuum pumps as claimed in the appended claims.

By providing the rotor and the end walls at oppositely facing surfaces,by annular recesses and annular ribs, respectively, wherein the ribs andthe recesses are interengaging so as to define radial clearances andaxial seals, respectively, between the end walls and the rotor, a pumpis obtained, which provides for a clearance between the rotor and endwalls irrespective of the materials thereof or any temperaturegradients, while the pump is simple and reliable and has very fewmovable parts. Very same end walls may be used in a large variety ofpumps having different pump capacities.

The rotor and the end walls may be provided with a plurality of annularrecesses and ribs, respectively, such that axial labyrinth seals betweenthe end walls the said rotor are obtained. In such manner any leakagesoccurring, are further reduced.

By axially biasing the rotor/drive shaft combination of the vacuum pump,preferably by means of axial stops provided in the end walls and aloaded spring, e.g. a cup spring, mounted between the rotor and theaxial stops, a vacuum pump, which is insensitive to axial forces isobtained. In such instance, a plurality of different transmissionsystems or gearboxes may be used with the vacuum pump. Further, anaxially biased pump is easier to manufacture, and the pump may bemounted upon a support, which is not horizontal.

Bearings, such as ball bearings, in which the rotor/drive shaftcombination may be mounted at the end walls would have a longerlifetime, be less noisy and cause less vibrations, when being axiallybiased. Further, the radial and axial plays of the bearings would notaffect the sealing properties of the inventive vacuum pump.

Further, by providing the end walls with a respective inner annular ribfor axially guiding the vanes when sliding substantially radially withinthe slots of the rotor, it is prevented that vanes may move sideways andget stuck at the inner corners of the end walls. Additionally, each ofthe inner annular ribs may be provided with a respective through holefor lubrication of the vanes.

By providing a rotor wherein the longitudinally extending radial slotsare at least partly, or completely, radially sealed at the longitudinalends thereof, the internal leakage is even further reduced. Hereby, thecasing and the end wall located at the motor side, may be an integratedsingle part.

Further characteristics of the invention and advantages thereof will beevident from the following detailed description of embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description of embodiments of the present invention givenhereinbelow and the accompanying FIGS. 1-3, which are given by way ofillustration only, and thus are not limitative of the present invention.

FIG. 1a is a front elevation view of a vacuum pump of the rotary vanetype according to prior art.

FIG. 1b is a sectional view along the line 1 b—1 b of FIG. 1a.

FIG. 1c is a radial cross sectional view of the vacuum pump of FIG. 1a.

FIG. 1d displays, in a perspective view, a rotor as being comprised inthe vacuum pump of FIG. 1a.

FIG. 1e displays, in a perspective view, a casing end wall as beingcomprised in the vacuum pump of FIG. 1a.

FIG. 2a is a front elevation view of a vacuum pump of the rotary vanetype when its front-end wall is demounted according to a firstembodiment of the present invention.

FIG. 2b is a sectional view along the line 2 b—2 b of FIG. 2a.

FIG. 2c is a radial cross sectional view of the vacuum pump embodimentof FIG. 2a.

FIG. 2d displays, in a perspective view, an inventive rotor as beingcomprised in the vacuum pump embodiment of FIG. 2a.

FIG. 2e displays, in a perspective view, an inventive casing end wall asbeing comprised in the vacuum pump embodiment of FIG. 2a.

FIG. 3a is a front elevation view of a vacuum pump of the rotary vanetype when its front-end wall is demounted according to a secondembodiment of the present invention.

FIG. 3b is a sectional view along the line 3 b—3 b of FIG. 3a, in whichalso fragmentary enlarged scale views of encircled portions are shown.

FIG. 3c is a radial cross sectional view of the vacuum pump embodimentof FIG. 3a.

FIG. 3d displays, in a perspective view, an inventive rotor as beingcomprised in the vacuum pump embodiment of FIG. 3a.

FIG. 3e displays, in a perspective view, an inventive casing end wall,and also a fragmentary enlarged scale view of an encircled portionthereof, as being comprised in the vacuum pump embodiment of FIG. 3a.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description, for purposes of explanation and notlimitation, specific details are set forth, such as particulartechniques and applications in order to provide a thorough understandingof the present invention. However, it will be apparent to one skilled inthe art that the present invention may be practiced in other embodimentsthat depart from these specific details. In other instances, detaileddescriptions of well-known methods and apparatuses are omitted so as notto obscure the description of the present invention with unnecessarydetails.

The vacuum pump of the present invention is primarily intended to beused with equipment such as an automatic milking machine and otherequipment present at a dairy farm. Nevertheless, the pump may besuitable for use in other fields, and as far as the present inventionconcerns there is no limitation whatsoever as to where the pump may findapplications.

With reference to FIGS. 2a-e a first exemplary embodiment of the vacuumpump of the present invention will be described.

The pump includes a cylindrical-shaped casing or casing 50, which has aninner cylindrical wall surface 52 and is closed at its opposite ends byend walls 54, 56 such as by means of machine screws 58 or the like,being received in holes 59 of end wall 54 and similar holes in thelongitudinal end of casing 50. Similarly, end wall 56 is mounted to theopposite end of casing 50. As shown, end wall 56 is integrated in alarger detail 57 referred to as a motor axle casing to be mounted to amotor casing housing a motor 200 for driving the pump. Further, casing50 includes circumferentially spaced apart fluid inlet 60 and outlet 62ports intercommunicating the interior cavity of the pump.

The rotor 64 of the machine is provided with a number of elongated vaneslots 66 cut therein on the radius thereof, and within these slots aremounted in freely slidable relation therein a plurality of vanes 68. Thepump drive shaft 70 is press-fitted into the rotor 64 (or otherwisekeyed thereto) and is rotatably mounted in the end walls 54, 56 as bymeans of bearings 72, 74. In an alternative version the rotor and thepump drive shaft are fabricated as a single unit. The bearings arepreferably slide fitted to the end walls 54, 56, and interference fittedto the rotor/drive shaft combination 64, 70.

The rotor 64 is concentrically mounted and positioned with respect tothe axis of the drive shaft 70 as shown in FIG. 2d, but the shaft 70 iseccentrically mounted relative to the cylindrical inner wall 52 of thecasing 50. Accordingly, it will be understood that for efficientoperation of a machine of this type, as the rotor turns within thecasing it is required for the outboard edges of the vanes 68 to be atall times in pressure-sealing contact with the inner surface 52 of thecasing 50 while reciprocatively sliding in the slots 66; and thatpressure losses around the ends of the vanes permitting escape of fluidto the exhaust, has also to be prevented.

To attain the aforesaid objectives, end walls 54, 56 are provided withannular recesses 84, 86 and the rotor 64 is provided with annular ribs88, 90 at its respective end faces. Recess 84 and rib 88 areinterengaging so as to define a radial clearance 92 and an axial seal94, respectively, between end wall 54 and rotor 64. Similarly, recess 86and rib 90 are interengaging so as to define a radial clearance 96 andan axial seal 98, respectively, between end wall 56 and rotor 64. Itshall be appreciated in this respect that a radial clearance signifies aplay between the rotor and the end walls, said play extending in theradial direction. Correspondingly, an axial seal signifies a thin slitor a gap between the rotor and the end walls, said thin slit or gapextending in the axial direction and operating as a seal between saidparts.

The rotor/drive shaft combination 64, 70 (joined in fixed relation orfabricated as a single piece) is axially biased by means of axial stops100, 102, respectively, provided in the end walls 54, 56 and a loadedspring, preferably a cup spring 104, mounted between rotor 64, or moreprecisely one of the bearings 74, and the axial stop 102 of end wall 56.In such manner the thermal expansion of rotor 64 is balanced by means ofspring 104 in the direction of end wall 56 (i.e. on the motor side).Such axial biasing is very advantageous since it allows for the use of acoupling (not illustrated), which generates axial forces. Preferablythen, the drive shaft 70 is provided with an axle spindle, to which thecoupling 201 is mounted, and via which the motor 200 can drive therotor/drive shaft combination 64, 70. Further, the use of axial biasingof the rotor/drive shaft combination 64, 70 provides for a moresilent-running pump with a longer lifetime.

End walls 54, 56 comprise a respective inner annular rib or ring 106,108 for axially guiding the vanes 68 when sliding substantially radiallywithin said slots. This guiding rib guides the vanes from theirinnermost position (e.g. at startup) towards their outermost positionwithout allowing them to move sideways and thus to possibly get stuck inthe end walls 54, 56. Annular ribs or rings 106, 108 may further beprovided with a respective through hole (not illustrated) forlubrication of the vanes.

The longitudinally extending radial slots 66 are in this embodimentpreferably extending along the complete longitudinal extension of saidrotor. The vanes 68 extend along the entire casing 50 and in thisrespect, an essentially radial sealing between vanes 68 and end walls54, 56 is provided as in the prior art device of FIG. 1. However, vanes68 are preferably made of a plastic or other low friction material, suchthat very small clearances between vanes 68 and end walls 54, 56 can beemployed. The need of lubrication of the vanes may in such instances bedispensed with. Further, the material of vanes 68 is preferably chosensuch that the thermal expansion of vanes 68 and of casing 50,respectively, are comparable. Further, vanes 68 are easily exchangeablesimply by demounting end wall 54, drawing the vanes axially out of theirrespective slots, inserting new vanes, and finally remounting end wall54.

Further notably, slots 66 are arranged not entirely radially, butparallelly translated therefrom, to be oriented in a radial-tangentialdirection. Such design is intended to be included in the expression“substantially radially” as used within the present patent application.Accordingly, vanes 68 are sliding in a substantially radial direction.

Advantages of this particular embodiment of the invention comprise:

An axial sealing is not working as a sliding bearing, which indicatesthat no lubrication is needed between rotor and end walls.

The location for lubrication of the vanes may be freely selected. Hence,the material of the vanes as well as the type of lubrication may be morefreely selected. Possibly, the pump may be driven entirely withoutlubrication.

The critical thermal expansion is now related to the diameter of therotor and not to the length thereof. Thus, there are possibilities tomanufacture pumps of longer lengths. Further, very same end walls may beused for both short and long vacuum pumps. Different materialcombinations for the casing, rotor, and end walls may be used with therisk of seizing reduced to a minimum.

The axial biasing of the rotor/drive shaft combination enables the useof a coupling, which generates axial forces.

The manufacturing will be easier due to less stringent tolerances.

The pump may be located on a surface, which is inclined with respect tothe horizontal plane.

The axial biasing of the rotor/drive shaft combination will result inlonger lifetimes of the ball bearings. Further, the bearings will causeless noise and less vibrations. The kind of bearings is more freelychosable and any radial and/or axial play of the bearings does notaffect the sealing between the rotor and the end walls.

In FIGS. 3a-e a second exemplary embodiment of the present invention isshown. This second embodiment is similar to said second embodiment andall identical parts and features of the two embodiments are givenidentical reference numerals in the Figures. However, the secondembodiment is differing from the first embodiment as regards thefollowing.

End walls 54′ and 56′ are provided with respective first and secondannular recesses 84′, 84″ and 86′, 86″, and rotor 64′ is provided withrespective first and second annular ribs 88′, 88″ and 90′, 90″ at eachof its longitudinal end faces. Thus, annular recesses 84′, 84″ and 86′,86″ and ribs 88′, 88″ and 90′, 90″ are interengaging so as to defineradial clearances 92′, 96′ and a plurality of axial seals 94′ 98′,respectively, between end walls 54′, 56′ and rotor 64′. Thus, axiallabyrinth seals are provided, which may further reduce the internalleakages of the pump.

End wall 56′ is as in previous embodiment integrated in a motor axlecasing 57′.

Annular ribs or rings 106′, 108′ as defined between respective annularrecesses 84′, 84″ and 86′, 86″ are adapted to guide the vanes 68 axiallywhen sliding substantially radially within the slots. Annular ribs orrings 106′, 108′ are further provided with a respective through hole(only through hole 110 in rib 106′ is illustrated, FIG. 3e) forlubrication of the vanes. Preferably, vanes 68, fluid inlet port 60, andthrough hole 110 for lubrication, are arranged circumferentially suchthat there are, at all times during operation, at least one of the vanes68 located between fluid inlet port 60 and the through hole 110 forlubrication. Thus, as through hole 110 never will be in opencommunication with inlet port 60 the internal leakages are furtherreduced.

Furthermore, the longitudinally extending radial slots 66 are at leastpartly, but preferably completely, radially sealed 112 at thelongitudinal ends thereof, e.g. by means of sealing rings 114, 116attached to the body of rotor 64′ by means of screws 118 or otherfastening means. Such sealing rings may extend along the entire radialextension of slots 66 as illustrated, or they may extend only partlyalong the radial extension of slots 66. Alternatively, the rotor 64′ ismade as a single piece with integrated radial seals.

Particular advantages of this latter embodiment comprise:

The internal leakage is further reduced.

A larger play between end walls and vanes may thus be acceptable, whichfacilitates the choice of vane material.

A larger “smallest distance” between the eccentrically arranged rotor64′ and the inner surface 52 of casing 50 may be acceptable. This wouldmake it possible to manufacture end wall/motor axle casing 56′, 57′ andcasing 50 integrated in a single piece.

Simpler manufacturing and logistics if tolerances are higher, fewerpieces are to be manufactured.

Simpler mounting if fewer pieces (integrated casing/end wall) are to bemounted.

No need of uniquely fastening end walls to casing by pins; the end wallsare thus exchangeable.

Simple and even lubrication of the vanes, if at all necessary, throughholes 110 provided in annular end wall ribs 106′, 108′.

It will be obvious that the invention may be varied in a plurality ofways. Such variations are not to be regarded as a departure from thescope of the invention. All such modifications as would be obvious toone skilled in the art are intended to be included within the scope ofthe appended claims.

What is claimed is:
 1. A vacuum pump of the rotary vane type comprising:a casing having a cylindrical inner wall surface; a first and a secondend wall at opposite sides of said casing defining a fluid cavitytherein; fluid inlet and outlet ports in open communication with saidfluid cavity; a rotor extending between said end walls and fixedlycarried by a drive shaft for rotation about an axis eccentric to saidcylindrical inner wall surface, said rotor being provided with aplurality of longitudinally extending substantially radial slots aboutthe periphery thereof; and a plurality of vanes, each beingsubstantially radially slidably carried within a respective one of saidslots, wherein at least one of said end walls and said rotor comprise,at oppositely facing surfaces, an annular recess and an annular rib,respectively, said rib and recess being interengaging so as to define aradial clearance and an axial seal, respectively, between said at leastone of said end walls and said rotor; said rotor/drive shaft combinationis rotatably mounted on said end walls via bearings provided betweensaid rotor and said end walls; and said rotor/drive shaft combination isaxially biased via axial stops provided on sides of said first andsecond end walls which face said fluid cavity, and a loaded springmounted between said rotor and the axial stop provided on the side ofone of said end walls.
 2. The vacuum pump of claim 1 wherein said springis a cup spring.
 3. The vacuum pump of claim 1 wherein said bearings areslide fitted to said end walls and interference fitted to saidrotor/drive shaft combination.
 4. The vacuum pump of claim 1 whereinsaid loaded spring is mounted between the axial stop of said one of saidend walls and one of said bearings.
 5. The vacuum pump of claim 1wherein said at least one of said end walls and said rotor comprise, atoppositely facing surfaces, a plurality of annular recesses and ribs,respectively, so as to define an axial labyrinth seal between said atleast one of said end walls and said rotor.
 6. The vacuum pump of claim1 wherein said other one of said end walls and said rotor comprise, atoppositely facing surfaces, an annular recess and an annular rib,respectively, said rib and recess being interengaging so as to define aradial clearance and an axial seal, respectively, between said other oneof said end walls and said rotor.
 7. The vacuum pump of claim 1 whereinone of said end walls comprises an inner annular rib for axially guidingsaid plurality of vanes when sliding substantially radially within saidslots.
 8. The vacuum pump of claim 1 wherein said plurality oflongitudinally extending radial slots are extending along the completelongitudinal extension of said rotor.
 9. The vacuum pump of claim 1wherein the casing and one of said end walls are an integrated singledetail.
 10. The vacuum pump of claim 1 wherein said bearings are ballbearings.
 11. The vacuum pump of claim 1 comprising a motor and acoupling, which generates axial forces, wherein said motor, via saidcoupling, is arranged for driving the rotor/drive shaft combination. 12.The vacuum pump of claim 11 wherein the drive shaft is provided with anaxle spindle, to which said coupling is mounted.
 13. The vacuum pump ofclaim 7 wherein said inner annular rib is provided with a through holefor lubrication of said plurality of vanes.
 14. The vacuum pump of claim13 wherein said plurality of vanes, said fluid inlet port, and saidthrough hole for lubrication, are arranged circumferentially such thatthere are, at all times during operation, at least two of said pluralityof vanes located between said fluid inlet port and said through hole forlubrication.
 15. The vacuum pump of claim 1 wherein said plurality oflongitudinally extending radial slots are at least partly radiallysealed at the longitudinal ends thereof.
 16. The vacuum pump of claim 15wherein said plurality of longitudinally extending radial slots arecompletely radially sealed at the longitudinal ends thereof.